Modern integrated circuits are made up of literally millions of active devices such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective chip. Electrical connections are made through bond pads to connect the chip to a package substrate or another die. Bond pads can be used for wire bonding or flip-chip bonding. Flip-chip packaging utilizes bumps to establish electrical contact between a chip's input/output (I/O) pads and the substrate or lead frame of the package. Structurally, a bump is disposed on the surface of a semiconductor substrate. The bump is then treated to maintain its position on the semiconductor substrate.
In addition to Flip-chip packaging, wafer level chip scale packaging (WLCSP) is currently widely used for its low cost and relatively simple processes. In a typical WLCSP, post-passivation interconnect (PPI) lines such as redistribution lines (RDLs) are formed on passivation layers, followed by the formation of polymer films. Thereafter, bumps are disposed on the semiconductor wafer and are expected to maintain position at certain locations. Due to the miniature scale of modern integrated circuits, maintaining bump position has become a challenge. Bump bridging and/or shifting issues have been affecting the yield. As a result, there is a need to solve the above deficiencies.